The present invention relates to a LAN interconnecting apparatus such as a bridge in a token-ring network for transferring information between LANs.
A conventional LAN interconnecting apparatus such as a bridge operates only in a bidirectional (full duplex) manner. In other words, frames are transferred from one LAN to the other LAN and vice versa. An example of such a conventional LAN interconnecting apparatus is disclosed in U.S. Pat. No. 4,621,362.
When the inter-LAN frame transfer traffic is excessive, some of the frames are lost due to overrun, and the subsequent frequent re-transmitting operations deteriorate the situation. Mere addition of a conventional bidirectional interconnecting apparatus, however, does not effectively ameliorate such a situation. This is because there is no practical mechanism for efficiently distributing the load between the two interconnecting apparatuses. According to U.S. Pat. No. 4,621,362, each frame includes information for identifying one or more bridges through which the frame is to pass and information indicating the order of the bridges for processing the frame. Therefore, if two rings are interconnected by a plurality of parallel bridges, one bridge among these parallel bridges will be designated, thereby enabling a frame to be transferred between the rings without confusion in spite of the presence of the parallel bridges. The above U.S. patent, however, does not teach which bridge should be designated in each frame in order to equalize the load of the parallel bridges.
Various mechanisms could be adopted for distributing load between the bidirectional interconnecting apparatuses. Such mechanisms, however, must be inevitably unsatisfactory in that they result in a considerable increase in the amount of: hardware and/or software, system complication, lack of flexibility, or inefficiency in load distritution.